1. Field of the Invention
This invention relates to improvements in aqueous resin systems based on melamine resins and/or urea-formaldehyde resins which are used for stabilizing rock and for plugging cavities.
2. Discussion of Related Art
The improvement of rock strength by injection of auxiliary chemicals typically made up with water is an old and multifarious problem. Various suspensions, emulsions or solutions are available as sealing and stabilizing media. Cement and inorganic sodium silicates are basically inexpensive and economical, but can only be sensibly used where rock permeability is sufficiently high and few, if any, aggressive waters are present. Improved working conditions and strength properties are obtained through the use of organic resins. The resins may be used in the form of solutions and/or suspensions and/or emulsions, considerable possibilities in regard to the modification of strength, viscosity, adhesiveness of the stabilizing material to the rock and the like being afforded by the particular choice of the resins. Various types of resins have been proposed for the purpose in questions, including for example epoxy resins, polyurethanes and other thermoplastics and thermosets.
Today, particular significance is attributed to systems based on polyurethanes of the type described, for example, in the journal "Gluckauf", 112 (1976), 803-807. On account of the high toxicity of isocyanates, however, these systems are being used increasingly less for ecological reasons.
Melamine- and urea-formaldehyde resins have also been proposed, normally being injected in aqueous solution or suspension into the rock to be cemented where they cure in largely predeterminable times under the effect of a catalyst applied at the same time. The catalysts used for the resins in question are acidic and/or alkaline systems, particular significance being attributed to the acidic systems and, among these, to the mineral acids. The prior art relating to improvements in rock strength by chemical injections, particularly in connection with the plugging of oil and gas wells, is represented for example by DE-AS 11 53 698 and by the Article by H. Barthel "Verbesserung der Gebirgsfestigkeit durch chemische Injektionen (Improving Rock Strength by Chemical Injections)", Bergb.-Wiss. 17 (1970), No. 8, 281 to 285.
A technological difficulty attending the use of melamine- or urea-formaldehyde systems lies in the instability of aqueous preparations of such resins which, even in the absence of acidic catalysts, undergo a considerable increase in viscosity relatively quickly, so that their processability is impaired. In particular, the injectability and penetrative power of the injected resin solution are increasingly impaired. In practice, therefore, the resin solutions or suspensions to be applied are prepared immediately before use and have to be applied relatively quickly thereafter.
The problem addressed by the present invention was to find a way of substantially improving the stability in storage of aqueous resin preparations of the type in question based on melamine- and/or urea-formaldehyde resins. This was to be possible even when the active substance contents of the aqueous preparations were, desirably, relatively high at more than 50% by weight, for example in the range from about 60 to 75% by weight.